1. The Field of the Invention
The present invention relates to an apparatus and method for detecting occlusions during delivery of a solution to a patient. More particularly, the present invention relates to a sensor having a flexible, waterproof barrier that may be used in connection with an infusion or feeding pump to prevent damage to the pump in the event of a fluid leak or spill.
2. State of the Art
Treating a patient often requires administering to the patient certain fluids, medication or other nutrients in solution form. The physical condition of a patient may require enteral feeding of a nutrient solution into a patient's stomach or bowel. Likewise, a patient may require parenteral or intravenous infusion of medication, hydration and/or nutrients.
In enteral feeding it is important to provide the solution, which can be somewhat viscous, within a desired pressure range to ensure the solution is delivered, but at a pressure which is not uncomfortable to the patient or which could damage tissue surrounding the outlet of the feeding set. While controlling pressure is a concern, medical personnel must also be concerned about possible occlusion of the feeding set which prevents delivery of the feeding solution. This can be caused by a blockage within the feeding tube as may be caused by materials in the feeding solution, or externally by the feeding set being crimped or otherwise obstructed by the patient or some other cause.
Likewise in parenteral and IV administration, it is important to deliver the solution accurately to the patient as the patient may require the medication, fluids or nutrition in the infused solution in order to survive. As with enteral feeding, the infusion of solutions parenterally should be done at a pressure low enough to avoid discomfort or damage to the veins, while at sufficient pressure to assure delivery of the solution. Likewise, it is also important to ensure that flow of the solution has not been occluded, as this may prevent the patient from receiving necessary hydration and medication for treating various conditions.
One method of delivering medications and other solutions is by using a feeding or infusion pump. (For ease of reference, both enteral feeding sets, parenteral feeding sets and IV infusion sets, and their associated pumps, are referred to herein as infusion pumps and infusion sets. Any use of “infusion pumps” and “infusion sets” shall be deemed to incorporate enteral, parenteral, and IV applications unless specifically noted to the contrary).
Infusion pumps are designed to deliver controlled doses to the patient, thus allowing medical personnel to monitor and control the amount of nutrition, hydration and/or medication which the patient is receiving. However, use of an infusion pump introduces risk that flow of a solution through the tubing may become impeded, resulting in the patient not receiving needed fluids and medications. For example, a patient may unintentionally roll onto the tubing thereby kinking or compressing the tubing and stopping or reducing the flow. Likewise a blood clot or other debris may block the flow of solution through the tubing.
To overcome these types of problems standard safety features on modern infusion sets include sensors to detect changes in flow of a solution through the tubing and to warn medical personnel when flow through the tubing is impeded. Some sensors on modern infusion sets detect occlusions by measuring a force exerted within the tubing of the infusion set. For example, if an occlusion occurs downstream of the infusion pump then the pressure inside the tubing downstream from the pumping mechanism will increase and the flexible tubing will expand. Expansion of the tubing exerts a force on the sensor that detects the increased pressure as a downstream occlusion. Alternatively, if an occlusion occurs upstream of the pumping mechanism, pressure inside the tubing (between the occlusion and the pumping mechanism) will generally decrease causing the flexible tubing to exert less force on the sensor than would normally be exerted when the infusion set is operating properly. This decrease in force will reduce the actual amount of solution which is being delivered to the patient and will be detected by the sensor as an upstream occlusion. If the pressure in the tubing falls outside of a predetermined range, the sensors will generally cause an alarm to sound indicating the presence of an occlusion. If the pressure changes do not fall outside the desired range, the pressure change may still be used to alter the cycles (typically either duration or frequency of cycles) of the pumping mechanism as the pressure has an effect on the amount of solution which is pumped during each cycle.
Another problem that medical personnel must be concerned with when delivering solutions to a patient using an infusion set is contamination or damage to the pumping mechanism. Although the tubing and cassette of an infusion set is discarded after use with a particular patient, the pump which drives the solution through the infusion set may be used with subsequent patients. While the outer surfaces of the infusion set can be easily sanitized with cleaning agents, it may difficult to clean the interior of the pump.
Likewise, while an infusion set is typically sealed, infusion pumps are used in a medical environment where solutions may be spilled on the pump. To prevent damage to the electronics of the pump, including the pressure sensors, a sealing mechanism is typically required.
To ensure that that the interior of the pump does not become contaminated and to prevent liquids from damaging the electronics, infusion sets often include seals that prevent liquid and bacteria from entering or exiting inner surfaces of the pump that are more difficult to routinely clean. To this end, the sensors (or external portions thereof) are often protected with a sheath of elastomeric material to prevent solution from contacting the sensor should a leak occur. This elastomeric material also provides a microbial barrier to make the pump easier to sanitize to ensure that cross-contamination does not occur with subsequent usage of the pump.
An example of such an elastomeric membrane disposed between the tubing and a rod associated with the sensor can be seen in U.S. Pat. No. 5,989,222. While the membrane helps to shield the rod from fluids, the elastomeric membrane also deforms somewhat under the changing pressuring in the tubing and thus may decrease the sensitivity of the sensor by absorbing all or some of the change in force exerted by the tubing.
Thus, there is a need for an improved sensor for detecting occlusions in an infusion set. The sensor's ability to detect a force exerted by the tubing of the infusion set should be maximized while providing a microbial barrier for patient protection and protecting the sensor from damage in the event a solution leaks from the infusion set or is otherwise spilled on the pump. It is also desirable to provide such a device which is relatively inexpensive and easy to use.